This invention relates to apparatus for treating sewage sludge in a hyperbaric vessel in which the sludge is oxygenated by injecting an oxygen-rich gas into the sewage sludge and then dispersing the mixture of sludge and oxygen-rich gas into the upper portion of a hyperbaric vessel for further interaction with an oxygen-rich atmosphere.
Traditionally, sewage, and specifically sludge, has been difficult to treat because it is, almost by definition, extremely variable in composition. In addition to human liquid and solid organic waste, the sludge to be treated in accordance with the present invention may include industrial and commercial sludge which is susceptible to aerobic treatment. In general, the present invention provides a means and process for highly efficient interaction of sludge particles with an oxygen-rich gas, in the form of O.sub.2 gas (oxygen) and/or O.sub.3 gas (ozone).
The present invention is intended primarily for treatment of activated sludge, namely, waste from domestic, commercial and industrial sources which create a biologically degradable material. A batch of pH adjusted waste to be treated is mixed with an oxygen-rich gas, the mixture is divided into small droplets and the droplets are dispersed within a pressure vessel where they are oxygenated by being exposed to an oxygen-rich gas for a substantial period of time. The Biological Oxygen Demand (BOD) and the Chemical Oxygen Demand (COD) of the waste are substantially saturated and satisfied. The addition of ozone produces an almost complete destruction and elimination of coliform, fecal coliform, salmonella and other harmful bacteria from the batch of sludge being treated. Although the coliform and fecal coliform bacteria are not in themselves particularly harmful, when they are present, it is recognized that other harmful bacteria are present. Thus, when the coliform and fecal coliform bacteria are destroyed, it is an indication that the other harmful bacteria, which are more difficult to detect, are also destroyed.
The present invention is intended to be used in a large scale sewage treatment system for treating activated sludge which is generally too thick to be treated efficiently on a large scale basis by presently existing commercial equipment. The present invention can be incorporated with presently existing wastewater treatment plants. Most existing wastewater treatment plants are capable of producing sludge with a solid content of about one and one-half percent by weight. The present invention has been designed to treat sludge having a solid content of greater than four percent to about six percent by weight, more preferably from about five percent to about six percent. The apparatus is believed to be most cost effective with sludge having solids content of about five and one-half percent to six percent by weight.
Various prior art references have dealt with treating sewage or water by aeration, oxidation or ozonation, as well as with dispersment in hyperbaric vessels. None, however, has all of the features of the present invention.
In U.S. Pat. No. 888,090 of Kestner, a centrifugal fan mixes and atomizes water and air using a centrifugal fan to purify the water. Water is fed coaxially within an air pipe which is mounted at the inlet end of a centrifugal fan so that the water and air are atomized by the fan.
U.S. Pat. No. 1,790,975 of Dallas et al. discloses a method and apparatus for treating sewage by the activated sludge process in which an air lift for circulating liquid in sewage treatment chambers are mixed as the air and sewage rises in a pipe to a distributor head which showers or sprays the liquid over the surface of the liquid in the chamber.
U.S. Pat. No. 3,271,304 of Valdespino et al. discloses mixing liquid sewage to be treated with pressurized air in a venturi-type aspirator in an open top treatment vessel. The venturi aspirator mixing device is located near the bottom of the treatment vessel substantially below the surface of the liquid being treated.
U.S. Pat. No. 3,650,950 of White discloses a device for treatment of waste materials in which various types of shearing rotors subject the liquid material to shearing stresses simultaneously with the injection of an oxidizing agent, such as ozone, to enhance biochemical and chemical treatment of the material, as well as to physically treat the material.
U.S. Pat. No. 3,772,188 of Edwards discloses a sewage and sludge treatment apparatus and process in which oxygen and ozone are bubbled through the material in a lower portion of a treatment vessel which may be a hyperbaric vessel. The oxygenated material is then pumped through a pipe against a distributor which distributes the treated material throughout an upper portion of the vessel for further contact with the oxygen-rich atmosphere.
Despite the disclosure in the above-identified patents of water, sewage or sludge treatment systems, a need existed in the sludge treatment industry for systems which more efficiently and completely oxygenated sludge of various compositions. This led one of the co-inventors of the present invention to develop a series of improved sludge treatment systems as illustrated, described and claimed in U.S. Pat. Nos. 4,487,699, 4,582,612, 4,659,464 and 4,695,388 of Charles A. Long, Jr., the disclosures of which are hereby incorporated by reference. While the sludge treating systems, processes and apparatus disclosed in the foregoing Long, Jr. patents enhanced the treatment of sludge compared to the systems, processes and apparatus previously known for that purpose, the present inventors devised a way to still further enhance the treatment of sewage sludge to reduce the bacteria in the treated sludge to below currently detectable levels in a relatively short time and in an efficient manner.
The present invention preferably is used with the same general types of systems used in the processes and apparatus disclosed in the foregoing Long, Jr. patents. Therefore, only the components of the overall system or reactor which are necessary to understand the present invention will be described herein.
By initially injecting oxygen or ozone gas into the sludge prior to dispersing the sludge in the form of several streams of divided drops, droplets or particles in a pressurized, oxygen-rich atmosphere through a plurality of channels formed in a combination gas and sludge mixing and dispersing means, more efficient and complete bacterial kill, oxygenation and activation of the sludge is obtained. The initial contact of the sludge with the pressurized oxygen-rich gas, and particularly ozone, into the separated stream of sludge within the channels of the combination gas and sludge mixing and dispersing assembly creates an intimate, immediate contact of a relatively high concentration of the oxygen-rich gas with the sludge to enhance the oxidation of the sludge. When the mixture is dispersed in the form of droplets or the like from the combination mixing and dispersing apparatus in a plurality of streams into the upper portion for interaction with the pressurized oxygen-rich gas, the previously oxygenated sludge is even further activated as the sludge is dispersed throughout the upper portion of the hyperbaric vessel.